1. Field of the Invention
The present invention relates generally to radio communication systems, and more particularly to receivers for ultra wide bandwidth (UWB) systems.
2. Discussion of the Background
With the release of the “First Report and Order,” Feb. 14, 2002, by the Federal Communications Commission (FCC) FCC 02-48, incorporated herein in its entirety, interest in ultra wide bandwidth (UWB) communication systems has increased. UWB communication systems spread information over a wide bandwidth of at least 500 MHz. Due to this spreading operation, the power spectral density, and thus the interference to narrow bandwidth receivers is small.
Conventional transmitted reference UWB (TR-UWB) systems such as discussed in R. Hoctor and H. Tomlinson, “Delay-hopped transmitted-reference RF communications,” Proceedings of the IEEE Conference of Ultra Wideband Systems and Technologies 2002 (UWBST'02), pp. 265-269, Baltimore, Md., May 2002, N. v. Stralen, A. Dentinger, K. Welles II, R. Gaus, R. Hoctor, and H. Tomlinson, “Delay hopped transmitted reference experimental results,” Proceedings of the IEEE Conference of Ultra Wideband Systems and Technologies 2002 (UWBST'02), pp. 93-98, Baltimore, Md., May 2002, F. Tufvesson and A. F. Molisch, “Ultra-wideband communication using hybrid matched filter correlation receivers,” Proc. IEEE Vehicular Technology Conference (VTC 2004 Spring), Milan, Italy, May 17-19, 2004, J. D. Choi and W. E. Stark, “Performance of ultra-wideband communications with suboptimal receivers in multipath channels,” IEEE Journal on Selected Areas in Communications, vol. 20, issue 9, pp. 1754-1766, December 2002, (each of which is incorporated herein in its entirety) relax the stringent timing requirements of the impulse radio (IR) systems, as discussed M. Z. Win and R. A. Scholtz, “Impulse radio: How it works,” IEEE Communications Letters, 2(2): pp. 36-38, February 1998, incorporated herein in its entirety, and do not need any channel estimation, which is a challenging task for coherent UWB receivers, as discussed in V Lottici, A. DAndrea, and U. Mengali, “Channel estimation for ultra-wideband communications,” IEEE Journal on Selected Areas in Communications, vol. 20, issue 9, pp. 1638-1645, December 2002, which is incorporated herein in its entirety.
Conventional impulse radio systems have used pseudo-random polarity codes to modify the data pulses, for example according to E. Fishler and H. V Poor, “On the tradeoff between two types of processing gain,” Proceedings of the 40th Annual Allerton Conference on Communication, Control, and Computing, Monticello, Ill., Oct. 2-4, 2002, which is incorporated herein in its entirety. Use of pseudo-random polarity codes helps reduce the spectral lines in the power spectral density of the transmitted data pulses in impulse radio signals, for example as discussed in Y.-P. Nakache and A. F. Molisch, “Spectral shape of UWB signals influence of modulation format, multiple access scheme and pulse shape,” Proceedings of the IEEE Vehicular Technology Conference, (VTC 2003-Spring), vol. 4, pp. 2510-2514, Jeju, Korea, April 2003, which is incorporated herein in its entirety.
Problems with conventional TR-UWB systems and apparatuses, for example as proposed in Hoctor, include a waste of energy on the reference pulses and the effect of using a noisy template signal which causes a large noise-noise term. To reduce the effects of the noise-noise terms, conventional approaches have been proposed to first pass the received signal through a matched filter (see Tufvesson), or to perform an averaging operation (see Choi). However, conventional approaches disadvantageously rely upon a delay line for signal detection.
FIG. 8 shows an example of a conventional TR-UWB receiver. In this example, a received signal r(t) is passed through a matched filter 802. The convention matched filter 802 is designed to match the entire incoming signal and assumes that data and reference pulses are always ordered the same way (i.e., data pulse is always first, or reference pulse is always first). An impulse response of the conventional matched filter 802 is equal to ctemp(−t), where the filter is matched to the sequence of the reference pulses for the related information symbol. The output of the matched filter 802 is delayed by delay line 804 and the delayed output is multiplied with the undelayed output of the matched filter 802 by multiplier 806. The delay amount is the delay time between first and second pulses in a frame of the received signal. The output of the multiplier 806 is passed through an integrator 808 to produce an output that is averaged over at least one chip time in the received signal. The output of the integrator 708 is passed through a sign detector 810 to produce an estimated data bit b.